Method and device for guiding a paper web or the like

ABSTRACT

The invention relates to a method and device for guiding a paper web, or corresponding web-like moving track, by using jets of compressed air as an aid. There are two jet directions, one essentially facing the arrival direction of the web ( 1 ) and the other essentially facing the departure direction of the web ( 1 ), in which case the jets form an area of vacuum between them. Compressed air is fed from one or more inlet ducts ( 3, 6 ).

The present invention relates to a method and device for guiding a paper web or the like. In general, this concerns guiding the web with the aid of air jets.

In a modern paper machine, there are numerous rolls and felts arranged as individual rolls, pairs of rolls, or series of rolls, depending on their position and purpose. In connection with many rolls, means are arranged to assist in removing water from the stock used in papermaking, thus resulting in the desired quality grade and the desired type of paper, which is finally reeled for later processing and use. The most, usual means of this kind are roll grooving, roll heating, and the introduction of a vacuum to the rolls. Also used are special highly absorbent felts, the water absorbed in which being removed during circulation for reuse.

A paper web made from stock is a very long totality, which, in the various stages of papermaking, must be transported around, or between numerous rolls. The rolls are situated over the entire length of the paper machine, at both the wet and dry ends, and are especially numerous in the paper machine's drying section, in which the rolls, around which the paper web travels, are usually in two rows.

If the paper web breaks for one reason or another, or if some other disturbance occurs, the paper web must be fed again to travel through the machine. Most of the paper web coming from the wet end is led to the pulper and a powerful, sharp water jet, for example, is used to cut and thus separate from the web a so-called web-threading tail, which is then attempted to be threaded through the machine and, if this succeeds, the tail is widened so that finally the full-width web travels through the machine, and is reeled as completed paper after the drying section.

Traditionally, a tail-threading rope, which conveys the web-threading tail forward in and through the drying section, has been used to carry the web-threading tail into the drying section, and indeed is still used in older machines. However, using a rope is very demanding and dangerous work, which will be prohibited by regulations due to be introduced.

Air jets are used for many purposes in paper machines. For example, air jets have been used to aid the separation of the paper web from a roll, while similarly air jets have also been used in many ways to guide the paper web.

Finnish patent 114491 discloses an example of a solution using an air jet to guide a paper web travelling through a drying section, and particularly to guide it from one roll to another in the drying section for the purpose of threading a web-threading tail. The said patent describes a method for carrying a paper web, usually a web-threading tail, from one roll to another, over a route in which a felt does not support the tail. In the method, four air nozzles are generally used, two of which are located on one side of the web and two on the other. On each side of the web, one air nozzle blows air in a direction nearly opposite to the direction of travel of the web while another nozzle blows air in nearly the same direction as the direction of travel of the web. This is claimed to carry the web steadily to the next roll.

While the aforementioned construction may be indeed very functional, it is, however, relatively complicated and requires accurate positioning on the opposite sides of the web. On the other hand, however, it appears that the said arrangement will not achieve very great precision in the lateral control of the web threading tail.

In addition, the use, in the drying section of a paper machine, of an air jet oriented in two different directions is known from U.S. Pat. Nos. 5,987,777 and 6,145,217. The drying section is equipped with a belt, on the surface of which the fibre web travels. In the first of the publications referred to, the air jets are intended on the one hand to detach the web from a roll in the conventional manner and on the other hand to hold the web on the conveyor belt.

In the second of the publications referred to, numerous air jets are used with the intention of guiding the free travel of the fibre web in the area between two rolls in a two-row drying section. The supposition is that, if a sufficient number of air jets are set to blow on different sides of a fibre web, the web will remain straight and travel in the direction in which the main flow of the air jets carries it.

Though certain parts of the solutions known from the two aforementioned publications function, the operation of certain other parts is highly uncertain. In neither of the publications is the intention to create a vacuum, nor is it to guide a material web accurately with the aid of the vacuum created.

The present invention is intended to create a method and device particularly for guiding the movement of a paper web simply and functionally. The intention is also particularly to position the web laterally in a sure manner.

The aforementioned and other benefits and advantages of the present invention are achieved by means of a method and device, the characteristic features of which are stated in the accompanying Claims.

In the following, one embodiment of the invention is described in great detail, with reference to the accompanying drawings, which show one well-regarded application of the invention.

Thus:

FIG. 1 shows a side view of the general positioning of the invention for guiding a web;

FIG. 2 shows a second embodiment of the invention as a view like that of FIG. 1;

FIG. 3 shows one practical embodiment of the use of the invention in connection with a separation roll; and

FIG. 4 shows the use of the embodiment of FIG. 3 in a real operating environment.

Thus, FIG. 1 shows a general view of the operating principle of the device according to the invention. The web 1, no matter whether it is a paper web or some other web, arrives in the immediate vicinity of the device. As will become clear from the later description, the direction of travel of the web is of no real r significance. The surface 2 is a suitable stop for the web 1. As will be described later, the surface 2 can be formed by, for example, the surface of a detaching blade. The surface 2 is at least as wide as the web being guided.

FIG. 1 shows that, under the surface 2, there is a duct 3, into which compressed air is led, running at essentially right angles to the direction of travel of the web 1. The air tries to leave the duct 3 through perforations or gaps 4 and 5. The air blown through these holes 4 and 5 is oriented in such a way that part of the airflow is oriented towards the arrival direction of the web 1 and part towards the departure direction of the web. The difference in the feed directions of the air fed from the duct 3 is less than 180 degrees. For reasons of clarity, in FIGS. 1 and 2 this difference is drawn to appear greater than it would be in a practical embodiment.

The air jets (which are marked with arrows in the figures) from ducts 4 and 5 create a vacuum in the area between the blast points. This means in turn that the web tends to be pulled by the vacuum to move towards the surface 2 and possibly onto it thus sliding along the surface. In this way, the web also travels forward in a manner that is laterally both controllable and stable. Here the actual transportation of the web is not interfered with, but is handled using conventional technology.

The positioning of the air-jet nozzles is very important in terms of the invention. The undisturbed transportation of the web in the manner shown by the invention cannot be achieved, if the ducts are formed with the aid of pipes that clearly rise above the surface 2. In such a case, the web would probably not travel at all along the surface between the airjet nozzles. The nozzles are therefore placed directly on the surface 2, or in shoulders slightly below it, as described in the following.

Further, in the publications referred to in the review of the prior art, it is possible that some kind of zone of lower pressure will arise in the area between the air jets blowing in two directions. However, in this case the paper web is not intended, as it is in the present invention, to be substantially sucked onto a smooth and slippery surface between the nozzles, but rather to be kept floating at a distance form the nozzles.

The relative strengths of the air jets can be easily controlled by adjusting the size of the flow ducts 4 and 5. Adjustment can also take place using a suitable control element, by means of which the cross-sectional area of at least one of the ducts 4 or 5 can be altered. Such control elements are not, however, drawn in the figures.

FIG. 2 shows the principle of a second embodiment. It differs from the first embodiment only in that air is fed to the ducts 4 and 5 from different feed ducts 3 and 6. Each duct 3 and 6 can be adjusted separately relative to the flow, for which reason it is also very easy to implement adjustment of the mutual strengths of the air jets discharging from the ducts 4 and 5.

Though in this case the surface 2 shown by FIGS. 1 and 2 is drawn straight, the shape of the surface is in no way restricted to that shown. In practical embodiments, the shape of the surface may even vary very greatly, according to its intended purpose. However, the essential factor is that there are no protrusions hindering movement in the area between the air jets, but instead the construction permits the web to move smoothly. Further, the surface must not allow any substantial amount of air to pass through it, so as avoid endangering the creation of the vacuum.

In practical tests, the principle of the invention has been shown to function well. The vacuum sucks the web into a firm grip and lateral stability is excellent.

FIG. 3 shows the use of the principle according to the invention in connection with a detaching blade 7. The detaching blade surface 8 is positioned against the roll, from which it is wished to detach the web. The airflows fed by the air ducts 3 and 6 from holes 4 and 5 create a vacuum between them, so that the web detaching from the roll becomes guided by the vacuum. As the figure clearly shows, the holes 5 are located in a shoulder 11. In this particular embodiment, the ducts 4 also terminate in a kind of shoulder 12.

FIG. 4 shows a practical application, in which a detaching blade 7, which is attached to frame structures 10 suitable for this purpose, is detaching the web from a roll 9. The edge 8 of the blade lies against the surface of the roll 9. Compressed air fed to ducts 3 and 6 discharges from perforations at the points shown by the arrows. The vacuum sucks the web into its grip at about the point shown by the triangular arrow and the web is guided in a stable manner to the next location. For example, in the drying section of a paper machine, the web travels in a known manner over very many rolls, so that there are numerous locations at which it must be guided.

The direction of the air jets, shown in FIGS. 1 and 2, is wrong for many practical embodiments, the angle between the jets being too small. In many applications, it is appropriate to align the air jets in opposite directions, so that the jets form at least nearly a straight angle (180 degrees). Powerful air jets will also create a vacuum between them even when they blow in essentially opposite directions. However, depending on the situation, the angle between the jets can be reduced even considerably. The search for the correct blast angle takes place by case-specific evaluation.

Though reference is made above to only a paper web, the invention is in no way restricted to that. Any web-like material whatever, which is not entirely permeable by air, can be guided using the method and basic apparatus described. 

1. Method for guiding a paper web, or corresponding web-like moving track, by using jets of compressed air as an aid, characterized in that the web is guided with the aid of a vacuum created on the surface (2), or in the immediate vicinity of the area between two air-jet discharge openings that are oriented essentially in the arrival direction of the web and in the departure direction of the web.
 2. Method according to claim 1, characterized in that the surface between the discharge ducts (4, 5) of the air jets is made to be essentially flat and impermeable by air.
 3. Method according to claim 1, characterized in that a single inlet duct (3) and two air-jet ducts (4, 5) leading out of it in two directions are used to feed the compressed air.
 4. Method according to claim 1, characterized in that two separate inlet ducts (3, 6), which feed air in two different directions, are used to feed the compressed air.
 5. Method according to any of the above claims, characterized in that the air-jet ducts (4, 6) are located over essentially the entire width of the web being guided.
 6. Method according to any of the above claims, characterized in that the air is fed through air-jet nozzles located in shoulders (11, 12).
 7. Device for guiding a paper web, or corresponding web-like moving track, by using jets of compressed air as an aid, characterized in that in the device there are compressed-air jet nozzles (4, 5) on either side of a surface that is essentially impermeable by air, of which the nozzles on one side are oriented essentially in the arrival direction of the web (1) and the nozzles on the other side are oriented essentially in the departure direction of the web (1), which jets form an area of vacuum between them.
 8. Device according to claim 7, characterized in that the air-jet nozzles (4, 5) are located on the two sides of an essentially smooth surface (2), the nozzle surfaces of the jets being essentially on or below the plane of the surface.
 9. Device according to claim 7, characterized in that there is only one inlet duct (3) for feeding the compressed air to the jet nozzles.
 10. Device according to claim 7, characterized in that there are two inlet ducts (3, 6) for feeding the compressed air to the jet nozzles.
 11. Device according to claim 7, characterized in that the air-jet nozzles are formed of rows of jet holes located on the surface (2) and essentially transversely to the direction of travel of the web being guided.
 12. Device according to claim 7, characterized in that the air jets feed by the jet nozzles form mutually approximately a straight angle.
 13. Device according to claim 7, characterized in that the discharge openings of the airjet are located in shoulders (11, 12). 